1. Field of the Invention
The present invention relates to a disc drive device for driving rotation of a CD-ROM, magneto-optical disc, and other disc media.
2. Description of the Art
For example, a disc drive device disclosed in FIG. 1 of Japanese Patent Publication No. 9-231674A has a plastic turntable mounted on a shaft of a spindle motor. This turntable is provided with a disc hole engagement projection with an outer circumference formed into a conical surface shape and with which a center hole of the disc is engaged, three through holes passing through the outer circumference of the disc hole engagement projection in the vertical direction at intervals of 120°, and a centering mechanism comprising flexible cantilever beams in the through holes extending outward in a diametrical direction from the disc hole engagement projection.
The center hole of a disc drops over the disc hole engagement projection, whereby the flexible cantilever beams are bent downward while the center of the disc approaches the center of the shaft. Due to this, the front end sides of the flexible cantilever beams resiliently contact the edge of the center hole and the disc is centered. For this reason, even if there is some variation in the diameter of the center hole of the disc, that variation is absorbed by the degrees of the bending amounts of the flexible cantilever beams.
The front end sides of the flexible cantilever beams resiliently contact and prop up the edge of the center hole, so, in addition to the centering function of the disc, also act to hold the centered state when a biased load is applied to the disc due to vibration etc. of the disc drive device at the time of turning of the turntable after that (centering holding function).
In actual circumstances of high speed driving of the turntable of for example 10,500 rpm or more, however, since there are only three flexible cantilever beams explained above at intervals of 120°, the centering holding function is insufficient. This becomes a factor of degradation of read/write precision and characteristics of a pick-up.
In order to eliminate this insufficiency of the centering holding function, an increase of the number of flexible cantilever beams may be considered, but this type of turntable has an outside diameter of at most about 30 mm. The flexible cantilever beams are also made of plastic, so the flexible centering cantilever beams cannot be narrowed in beam width due to strength considerations. Further, an increased number of through holes would result in the disc hole engagement projection itself becoming relatively weak in strength. Therefore, the number of flexible cantilever beams is limited to at most six and the centering holding function remains inferior.
On the other hand, increasing the beam width of the flexible cantilever beams without increasing the number of the flexible cantilever beams that much may be considered. However, elastic deformation of the flexible cantilever beams is important, yet greater beam length cannot be secured, therefore the cantilever beams increase in bending rigidity and end up being reduced in resiliency. Further, if increasing the beam width, a creep phenomenon peculiar to a plastic easily occurs and a longer service life is difficult to secure.
The positions (angles) where the front end portions of the flexible cantilever beams resiliently contact the hole edge or hole walls of the disc hole are limited when viewed microscopically. Therefore, as broader the beam width are made, the more the resilient contacting positions (angles) will differ among the cantilever beams, so an inferior centering function will be caused.